Many land-born vehicles are designed for maximum internal volume coupled with minimum fabrication costs. These vehicles include freight trucks, semi-trailers, moving vans and trailers, as well as campers and the like. As a result of these two design requirements the vehicles have a rectangular or boxlike shape with bluff corners. Consequently, their shape produces a characteristically high aerodynamic drag at highway speeds. In an attempt to reduce this drag, several "add-on" devices have been developed which modify the flow pattern around the bodies and create a more streamlined contour of the vehicle. These add-on devices definitely increase the vehicle's efficiency and reduce the fuel consumption, and one such device is the subject of a patent for which applicant of the instant invention applied dated Mar. 18, 1976, U.S. Ser. No. 668,327. These add-on devices are uniformly passive and immobile in operation, although many of them are adjustable or movable to vary the shape or position prior to or between uses. Clearly, the apparently permanent increase in fuel cost and scarcity has spawned a renewed interest in drag reduction and the development of numerous variations of streamlining fairing structures to meet this need.